June 8, 2021 – A team from Lawrence Livermore National Laboratory (LLNL) took a closer look at how nuclear weapon explosions near the Earth’s surface create complications in their effects and apparent returns. Attempts to correlate event data with low burst heights have revealed the need to improve the theoretical treatment of strong shock waves bouncing off hard surfaces.
This led to an extension of the fundamental theory of violent shocks in the atmosphere, which was first developed by GI Taylor in the 1940s. The work represents an improvement in the basic understanding of the laboratory team. from the effects of nuclear weapons to near-surface detonations. The results indicate that the shock wave produced by a nuclear detonation continues to follow a fundamental law of scale when reflected from a surface, allowing the team to more accurately predict damage than a detonation will occur in a variety of situations, including urban environments.
The results, presented in Proceedings A of the Royal Society Publishing, are written by Andy Cook, Joe Bauer and Greg Spriggs. The work “The reflection of a shock wave by a very intense explosion” is also highlighted on the cover of the publication.
The paper demonstrates that the geometric similarity of the Taylor shock wave persists beyond reflection from an ideal surface. Upon impact on the surface, the spherical symmetry of the shock wave is lost but its cylindrical symmetry persists. Preserving axisymmetry, geometric similarity, and plane symmetry in the presence of a mirror-like surface causes all flow solutions to collapse when scaled by height d burst (HOB) and the time of arrival of the shock to the surface. The scaled explosion volume for any efficiency, HOB and ambient air density follows a single universal trajectory for all scaled time, both before and after reflection.
The team used the Miranda code and the Ruby supercomputer to compare the theory to numerical simulations, and verified that Miranda reproduced Taylor’s similarity solution for a strong shock wave in an ideal atmosphere.
“Before collecting data and collecting results, we did some convergence studies by refining the grid until the answer didn’t change,” Cook said. “Next, we performed a series of converged resolution simulations for different nuclear efficiencies, burst heights and ambient air densities. We found that the scaled blast volume in each case fell on the same non-dimensional curve. The simulations covered scales from a few millimeters to several kilometers. The largest simulations used 3,136 processors and lasted a week. “
The Strategic Consequence Analysis (SCA) team uses the Miranda code to simulate nuclear explosions in non-ideal environments. “Non-ideal air blast” refers to anything more complicated than the Nevada desert, for example, explosions over mountainous terrain or over water or in the presence of rain or snow. These environments modify the shock wave in an operationally significant way, which must be characterized by precise simulations. High-fidelity explosion simulations allow weapon designers to assess the effectiveness of particular designs for specific scenarios.
The team said understanding nuclear weapon explosions near the Earth’s surface is important to the nation.
“Having the ability to accurately predict damage from a high performance device in a wide range of cases, particularly in urban settings, is of paramount interest to our national security,” Spriggs said. “This information allows us to pre-calculate damage and guide emergency response personnel in the event of an attack from the United States or a catastrophic accident, such as the recent explosion in Beirut.”
The research arose out of decades of data collected by the Film Scanning and Re-analysis Project, hosted by the Laboratory’s Design Physics division within the Weapons and Complex Integration Directorate of the LLNL, with Spriggs being the principal investigator. . The work was also supported by the research and development program led by the laboratory of the LLNL and by the mission effectiveness program of the National Nuclear Security Administration.
“The more we know about the effects of nuclear detonations in different environments, the better prepared we will be to respond,” said Spriggs. “These new results lay the foundations for a more precise and complete theory of nuclear explosions interacting with the environment. Many other effects, gleaned from old atmospheric test films, have yet to be explained. “
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